This indicator simply changes the background and color of candle based on the previous candle's close. If a candle closes high than the previous candle's high it will be indicated via green coloring. If a candle closes lower than the previous candle's low it will be indicated in red coloring. Additionally, grey colored candles appear when neither occur - often signifying consolidation.
These candles can be used to identify previous small lasting and long ranging trends. Areas that are heavily saturated with one specific color will likely indicate a trend.
If you are not able to see the colored candles, disable your main candle overlay in the top left by clicking on the eye icon.